Molecular structure, spectral characteristics, and nonlinear optical properties of labetalol: an experimental and computational investigation

Labetalol is an antihypertensive agent that possesses both α- and β-adrenergic blocking properties. This characteristic allows for its clinical use in both chronic hypertension and hypertensive emergencies. In this study, the FT-IR, FT-Raman, 1 H, 13 C, and DEPT-135 NMR spectra of labetalol hydrochloride (Labetalol HCl) were recorded and examined. Furthermore, the pharmacologically active (R, R) stereoisomer of labetalol was theoretically investigated using the B3LYP functional and the 6-311++G(d, p) basis set. The theoretically determined ground-state geometry of the molecule showed excellent agreement with experimental data reported in the literature. Using the obtained optimized structure, the vibrational spectra of the molecule were simulated, and the vibrational modes were assigned by evaluating them together with the experimental data. Nuclear Magnetic Resonance (NMR) analysis of the molecule was performed considering experimentally recorded values and calculations for gas phase, DMSO, and chloroform solvent environments, and the chemical shift values for each H and C atom were determined. Using Time-Dependent Density Functional Theory (TD-DFT) and Solvation Model based on Density (SMD) approaches, the UV-Vis spectra of the molecule were obtained in the gas phase and in four different solvent environments (ethanol, methanol, DMSO, and water). To better understand the electronic properties of the molecule, Frontier Molecular Orbitals (FMO), Molecular Electrostatic Potential Surface (MEPS), Hirshfeld surface analysis, Mulliken and Hirshfeld charge distributions, and Density States (DoS) analyses were performed. In addition, the non-linear optical (NLO) properties of the molecule were theoretically calculated, and the results showed that the molecule could be a promising NLO candidate.